1. Field of the Invention
The present invention is directed to an energization control device for an electric motor such as a switched reluctance motor.
2. Related Art
In general, a switched reluctance motor (SR motor) includes a rotor from which a plurality of equally-pitched pole portions are outwardly extended in the radial direction and a stator from which a plurality of equally-pitched pole portions are inwardly extended in the radial direction. The rotor is formed of a plurality of stacked thin iron plates. The stator has a plurality of copper-made phase coils which are wound on the respective plurality of pole portions of the stator. In the SR motor, as is well known, each of the pole portions of the stator acts as an electromagnet and when each of the pole portions of the rotor is attracted by the electromagnetic force of the stator the rotor is brought into rotation. Thus, changing the energizing conditions of the respective phase coils in turn depending on the current angular position of the rotor makes it possible to rotate the rotor in a desired direction.
A conventional SR motor is disclosed in e.g. Japanese Patent Laid-open Print No. Hei.11(1999)-346494 and is made up of three phase coils arranged on a stator, one end of each of the phase coils being connected to one of high and low potential lines of a power supply by way of a first switching element, the other end of each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a second switching element, one end of the each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a first diode which allows current flow from the latter to the former, the other end of each of the phase coils being connected to one of the high and low potential lines of the power supply by way of a second diode which allows current flow from the former to the latter; angular position detection means for detecting an angular position of the rotor;
rotational speed detection means for detecting a rotational speed of the rotor;
actual current detection means for detecting an actual current which passes through each of the phase coils; and
control means determining an energization-on angle, a first energization-off angle, and a target current value, for each of the phase coils, on the basis of the rotational speed of the rotor and a target torque which is calculated based on externally inputted information, the control means approximating the actual current value to the target current value in such manner that, while the rotor rotates from the energization-on angle to the first energization-off angle, making one of the first and second switching elements and the other ON and OFF concurrently and making both the first and second switching elements ON concurrently are alternated.
In this conventional SR motor, within an angular range, even if the rotor exceeds the energization-off angle, a condition exists wherein one of the first switching elements and the second switching elements is made ON and the other is made OFF concurrently. However, in this conventional SR motor, when the first switching element and the second switching element are made OFF concurrently, the current flowing through each of the phase coils drops drastically. Thus, the stator and the rotor which are mutually attracted due to phase coil energization is suddenly released, thereby generating noise.
In view of the foregoing circumstances, a needs exists for overcoming the aforementioned problem and providing an energization control device for electric motors in which noise reduction is effectively established.
A first aspect of the present invention is to provide an energization control device for an electric motor which satisfy the request noted above and comprises:
a plurality of phase coils arranged on a stator, one end of each of the phase coils being connected to one of high and low potential lines of a power supply by way of a first switching element, the other end of each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a second switching element,
one end of the each of the phase coils being connected to the other of the high and low potential lines of the power supply by way of a first diode which allows current flow from the latter to the former, the other end of each of the phase coils being connected to one of the high and low potential lines of the power supply by way of a second diode which allows current flow from the former to the latter;
angular position detection means for detecting an angular position of the rotor;
rotational speed detection means for detecting a rotational speed of the rotor;
actual current detection means for detecting an actual current which passes through each of the phase coils; and
control means determining an energization-on angle, a first energization-off angle, and a target current value, for each of the phase coils, on the basis of the rotational speed of the rotor and a target torque which is calculated based on external information inputted, the control means making one of the first and second switching elements ON-OFF and the other ON while the rotor rotates from the energization-on angle to the first energization-off angle, and approximating the actual current value to the target current value, the control means determining a second energization-off angle on the basis of the target torque and the rotational speed of the rotor for each of the phase coils, the control means making both the first and second switching elements OFF concurrently while the rotator rotates from the second energization-off angle to the energization-on angle, the control means making one of the first and second switching elements ON-OFF at an arbitrary duty ratio and making the other OFF while the rotor moves from the first energization-off angle to the second energization-off angle.
In accordance with the first aspect of the present invention, both the first switching element and the second switching element are made ON when the rotor reaches the first energization-on angle, and one of the first and second switching elements is made ON-OFF and the other is made ON until the rotor reaches the first energization-off angle for establishing soft/hard chopping in accordance with the actual current value exceeding the target current value. When the rotor reaches the first energization-off angle, despite whether or not the actual current value exceeds the target current value, the second switching element is made OFF. The first switching element is made ON-OFF at a duty ratio for duty chopping until the rotor reaches the second energization-off angle. When the rotor reaches the second energization-off angle, both the first switching element and the second switching element are made OFF.
A second aspect of the present invention is to provide an energization control device, as a limited version of the first aspect, wherein the control means determines an intermediate energization-off angle between the first energization-off angle and the second energization-off angle, holds a condition under which one of the first and second switching elements is made ON and the other is made OFF concurrently while the rotor rotates from the first energization-off angle to the intermediate energization-off angle, and makes one of the first and second switching elements ON-OFF at an arbitrary duty ratio and makes the other OFF while the rotor moves from the intermediate energization-off angle to the second energization-off angle.
In accordance with the second aspect of the present invention, both the first switching element and the second switching element are made ON when the rotor reaches the first energization-on angle, and one of the first and second switching elements is made ON-OFF and the other is made ON until the rotor reaches the first energization-off angle for establishing soft/hard chopping in accordance with the actual current value exceeding the target current value. When the rotor reaches the first energization-off angle, despite whether or not the actual current value exceeds the target current value, the second switching element is made ON while the first switching element is made OFF for doing 0-volt loop chopping and such a condition remains unchanged until the rotor reaches the intermediate energization-off angle. When the rotor reaches the intermediate energization-off angle, the second switching element is made OFF. The first switching element is made ON-OFF at a duty ratio for duty chopping until the rotor reaches the second energization-off angle. When the rotor reaches the second energization-off angle, both the first switching element and the second switching element are made OFF.
A third aspect of the present invention is to provide an energization control device, as a limited version of the second aspect, wherein the control means makes one of the first and second switching elements ON-OFF at the duty ratio which is changed such that a ratio of an ON-time duration to an OFF-time duration is reduced with passing of time and makes the other OFF while the rotor moves from either of the first energization-off angle or the intermediate energization-off angle to the second energization-off angle.
In accordance with the third aspect of the present invention, the second switching element is made OFF when the rotor reaches the first energization-off angle or the intermediate energization-off angle, and until the rotor reaches the second energization-off angle the first switching element is made ON-OFF for doing duty chopping at a duty ratio which varies such that the percentage of an ON-time duration decreases with passing of time relative to an OFF-time duration.
A fourth aspect of the present invention is to provide an energization control device as a limited version of third aspect wherein one of the first energization-off angle and the intermediate energization-off angle which are originally determined is put ahead.
A fifth aspect of the present invention is to provide an energization control device as a limited version of the forth aspect wherein between the first energization-off angle to the intermediate energization-off angle the target current value is increased.